text: Heating hexachlorophosphazene to ca. 250 °C induces polymerisation. The tetramer also polymerises in this manner, although more slowly. The conversion is a type of ring-opening polymerisation (ROP). The ROP mechanism is found to be catalysed by Lewis acids, but is overall not very well understood. Prolonged heating of the polymer at higher temperatures (ca. 350 °C) will cause depolymerisation.
  The structure of the inorganic chloropolymer product (polydichlorophosphazene) comprises a linear – chain, where n ~ 15000. It was first observed in the late 19th century and its form after chain cross-linking has been called "inorganic rubber" due to its elastomeric behaviour.
  This polydichlorophosphazene product is the starting material for a wide class of polymeric compounds, collectively known as polyphosphazenes. Substitution of the chloride groups by other nucleophilic groups, especially alkoxides as laid out above, yields numerous characterised derivatives.